The invention relates to a low-pressure gas discharge lamp comprising a gas discharge vessel with a copper-containing gas filling, electrodes and means for generating and maintaining a low-pressure gas discharge.
Light generation in low-pressure gas discharge lamps is based on the principle that charge carriers, particularly electrons but also ions, are accelerated so strongly by an electric field between the electrodes of the lamp that collisions with the gas atoms or molecules in the gas filling of the lamp cause these gas atoms or molecules to be excited or ionized. When the atoms or molecules of the gas filling return to the ground state, a more or less substantial part of the potential energy is converted to radiation.
Conventional low-pressure gas discharge lamps comprise mercury in the gas filling and, in addition, a phosphor coating on the inside of the gas discharge vessel. A drawback of the mercury low-pressure gas discharge lamps resides in that mercury vapor primarily emits radiation in the high-energy, yet invisible UV-C range of the electromagnetic spectrum. This primary radiation must first be converted by the phosphors to visible radiation with a much lower energy level. In this process, the energy difference is converted to undesirable thermal radiation.
In addition, the mercury in the gas filling is being regarded more and more as an environmentally harmful and toxic substance that should be avoided as much as possible in present-day mass-products as its use, production and disposal pose a threat to the environment.
It is known already that the spectrum of low-pressure gas discharge lamps can be influenced by substituting the mercury in the gas filling with other substances.
For example, GB 2 014 658 A discloses a low-pressure gas discharge lamp comprising a discharge vessel, electrodes and a filling which contains at least a copper halogenide as the UV emitter. This copper halogenide-containing low-pressure gas discharge lamp emits in the visible range as well as in the UV range at 324.75 and 327.4 nm.
It is an object of the invention to provide a low-pressure gas discharge lamp the radiation of which is as close as possible to the visible region of the electromagnetic spectrum.
In accordance with the invention, this object is achieved by a low-pressure gas discharge lamp provided with a gas discharge vessel comprising a gas filling with a copper compound selected from the group formed by the oxides, chalcogenides, hydroxides, hydrides and metalorganic compounds of copper, and comprising a buffer gas, which low-pressure gas discharge lamp is further provided with electrodes and means for generating and maintaining a low-pressure gas discharge.
In the lamp in accordance with the invention, a molecular gas discharge takes place at a low pressure, which gas discharge emits radiation in the visible and near UVA region of the electromagnetic spectrum. Apart from the characteristic lines of copper at 325, 327, 510, 570 and 578 nm, said radiation also includes a wide continuous spectrum in the blue range of the electromagnetic spectrum from 400 to 550 nm. As this radiation originates from a molecular discharge, the type of copper compound, possible further additives as well as the internal pressure of the lamp and the operating temperature enable the exact position of the continuous spectrum to be controlled.
In combination with phosphors, the lamp in accordance with the invention has a visual efficiency which is substantially higher than that of conventional low-pressure mercury discharge lamps. The visual efficiency, expressed in lumen/Watt, is the ratio between the brightness of the radiation in a specific visible wavelength range and the energy for generating the radiation. The high visual efficiency of the lamp in accordance with the invention means that a specific quantity of light is obtained at a smaller power consumption. Besides, the use of mercury is avoided.
In a lamp comprising a gas filling containing a copper compound selected from the group formed by the oxides, chalcogenides, hydroxides, hydrides and the metal-organic compounds of copper, and containing a buffer gas, the gas discharge takes place with a very high radiant intensity per unit area. For this reason, the lamp in accordance with the invention can be advantageously used as a backlight for liquid crystal display screens.
For general illumination purposes, the lamp is combined with appropriate phosphors. As the losses caused by Stokes"" displacement are small, visible light having a high light output is obtained.
A further improved efficiency at lower operating temperatures is achieved if the gas filling comprises a mixture of a copper compound selected from the group formed by the halogenides, oxides, chalcogenides, hydroxides, hydrides and the metalorganic compounds of copper with a copper halogenide.
It may be alternatively preferred for the gas filling to comprise, as a further additive, a compound of thallium, which is selected from the group formed by the halogenides, oxides, chalcogenides, hydroxides, hydrides and the metalorganic compounds of thallium. As a result, a gas discharge with a wide continuous spectrum is obtained.
For the buffer gas the gas filling may comprise an inert gas selected from the group formed by helium, neon, argon, krypton and xenon.
Within the scope of the invention it may be preferred that the gas discharge vessel comprises a phosphor coating on the outside surface. The UVA radiation emitted by the low-pressure gas discharge lamp in accordance with the invention is not absorbed by the customary glass types, but goes through the walls of the discharge vessel substantially without any losses. Therefore, the phosphor coating can be provided on the outside of the gas discharge vessel. This results in a simplification of the manufacturing process.
Within the scope of the invention it is particularly preferred that the gas filling contains a copper compound, selected from the group formed by the oxides, chalcogenides, hydroxides, hydrides and the metalorganic compounds of copper, in a concentration in the range from 1 to 10 xcexcg/cm3, and argon at a partial pressure in the range from 1 to 10 mbar.